Process of producing crystalline aluminum sulphate



S SCOFIELD ET AL Li Q1 m Patented Aug. 5, 1924.

treated SEER-MAN w. SCOFIELD AND JOHN B. LA RUE, or CLEVELAND, 01110;sen) LA nun ASSIGNOR TO sAro soormrn.

PROCESS PRODUCING CRYSTALLINE ALUMINUM SULPHATE.

Original application filed September 2, 1920, Serial No. 407,724.Divided and this application filed May 17, 1922. Serial No. 561,703.

To all whom it may concern:

Be it known that we, SHERMAN W. Soo- FIELD, and J OHN B. LA Run,citizens of the United States, residents of Cleveland, couna ty ofCuyahoga, and State of Ohio, have invented new and useful Improvementsin Processes of Producing Crystalline Aluminum Sulphate, of which thefollowing is a specification, the principle of the invention beingherein explained and the best mode in which we have contemplatedapplying that principle, so as to distinguish it from other inventions.

Our invention relates to processes of producing crystalline aluminumsulphate and particularly relates to an improved method of changingaluminum hydroxide to a solution of aluminum sulphate and then obtaining from the latter crystalline aluminum sulphate. The subject matter ofthis application has been divided out of our pending application, SerialNo. 407,724, filed Sept. 2, 1920, upon improved processes of separatingthe constituents of mineral silicates.

The annexed drawing and the following description set forth in detailcertain steps embodying our invention, the disclosed steps, however,constituting but one of the various methods by which the principle ofthe said invention may be applied.

In said annexed drawing;

The figure is a partial elevation and partial central vertical sectionof a vacuum chamber utilized in the carrying out of our new and improvedprocess.

Referring briefly to the disclosure contained and claimed in the abovementioned application, Serial No. 407,724, from which the subject matterof this application has been divided out, and as showing how we obtainthe aluminum hydroxide which is reacted upon by the process of thisapplication, we Wish to state that we first crush crystallinepotash-feldspar or reduce the same to small. particles and then calcinethis feldspar until it is converted into an amorphous condition. In thisamorphous condition, the feldspar can be decomposed by a solution ofcaustic alkali at a high temperature and under pressure. We mix thecalcined amorphous feldspar with caustic alkali and water, preferably astrong solution of caustic potash, and seal the same tightly in adigester where the mixture is agitated and heated adequately for two orthree hours at a temperature of substantially 265 to 271 centigrade, thepressure rising to substantially 300$]: per square inch. substantiallycomplete digestion of the feldspar, except that some insoluble silicatesstill remain in the digester in crystalline form.

We continue the heat and the moisture in the digester commences to beabsorbed by the mass at the bottom of the digester, the insolublesilicates becoming fused. We add more water to the digester, accordingto the space that is afforded, causing the pressure to rise rapidly andthe digestion has then reached a point substantially 98% to 99%complete. After the heat has been shut off and the mass allowed to standfor substantially one hour, the digester contains a concentratedsolution of alkali-metal silicate and, alkali-metal aluminate. We addsuflicient water to the solution for the purpose of thinning it down toreceive carbonic acid gas by means of which silicic acid and aluminumhydroxide are precipitated and the solution contains potassiumcarbonate. This carbonization is eifected in a standard carbonater tankand the gas is introduced, in the cold, at a pressure slightly above anormal atmospheric pressure.

As to the proportions of the ingredients utilized during the carryingout of the afore described steps, We wish to state that substantially 4#of potassium feldspar can be treated with substantially 6# of potassiumhydroxide, the water first added to the digester being substantially 4#,and then 4:# more after the completefusion has taken lace.

p The potassium carbonate solution, obtained as a result of thecarbonating, is decanted oif, and the precipitate leached and theleaching water added to the decanted solution. We have thus recoveredthe potash value from the feldspar. The alumina and silica residue isthen treated with sulphuric acid in a lead-lined tank, resulting inobtaining soluble aluminum'sulphate and crystalline silicic acid. Thesolution of aluminum sulphate is decanted offand the-precipitate leachedand the leaching water added to the decanted solution. These steps haveresulted in the separation of the aluminum and silicon values containedin the potash. We

4 This initial action results in a and the temperature to drop,

crating pan, and adjacent have also thereby converted the aluminumhydroxide to a solution of aluminum sulphate, formin part of the processof this application, w 'ch sulphate will beextracted incrystalline formby the process and apparatus now to be described.

For the purpose of extracting the aluminum value in the form ofcrystalline aluminum sulphate, we utilize the following procedure, inconnection with the apparatus shown in the accompanying drawing. Thisapparatus consists of a standard vacuum tank 1, connected with a steampipe 2, running to an suitable source of supply for the steam, an acondenser 3, gauge 4, pump 9, etc. Inlets for the mother liquor 11,containing the aluminum sulphate, are indicated by the ordinal 5 andoutlets therefor b the ordinal 6. The chamber 1 is Jsubdivlded into anynumber of suitable compartments, A, B, C, etc., and in each compartmentis positioned a tray 7 forming an evapthe top of each compartment ascreen 8. By means of the inlets 5, the mother liquor 11, is introducedinto the tray 7, and the chamber is then subjected to a partial vacuumof from twelve (12) to twenty-five (25) inches mercury, according to theweight of the solution, and to steam heat so as to create a temperaturein the chamber 1, of from 78 to 100 Fahrenheit. This vacuum and heatresults in the liquor in the tray 7, shooting up into the screen 8, asshown in compartment A in the figure, resulting in the clinging ofaluminum sulphate crystals to the screens each time the solution shootsup and drops back, thus forming hanging columns 10, of these crystals,as shown in compartment B. This process continues until practically allof the aluminum sulphate in the mother liquor has been removed and is inthe form of crystals hanging to the screens 8. The mother liquor is thenwithdrawn from the chamber 1, by means of outlets 6, and returned to theleadlined tank and mixed with the next charge therein for the use ofsuch sulphuric acid as v of! the steps of may have remained in themother liquor. A substantially complete vacuum is then created in thechamber 1, and the crystals of aluminum sulphate thus dried.

The source of the aluminum sulphate solution is not material to ourimproved method of crystallizing the same but we have described hereinthe reacting of aluminum hydroxide with sulphuric acid merely asillustrative and because this step was one the whole improved processset forth in said application, Serial No.

407,724, for extracting the potash and other values from feldspar.

What we claim is 1. In processes of crystallizing aluminum sulphate outof; solutions of the latter, the step which consists in subjecting thesolution is thrown, said screen tion to a partial vacuum, causing it toboil violently, means being superposed above .the evaporating panagainst which the solution is thrown, said means catching the salt andretaining the same as back.

2. In processes of crystallizing aluminum sulphate out of solutions ofthe latter, the step which consists in subjecting the solution to apartial vacuum, causing it to boil violently, a screen being superposedabove the evaporating pan against which the solucatching the salt I1dretaining the same as the solution drops ack.

3. In processes of crystallizing aluminum sulphate out of solutions ofthe latter, the step which consists in subjecting the solution to apartial vacuum and to a temperature of from 78 to 100 Fahrenheit,causing it to boil violently, means being superposed above theevaporating pan against which the solution is thrown, said meanscatching the salt and retaining the same as the solution drops back.

4. In processes of crystallizing aluminum sulphate out of solutions ofthe latter, the step which consists in subjecting the solution to apartial vacuum and to a temperature of from 78 to 100 Fahrenheit,causing it to boil violently, a screen being superposed above theevaporating pan against which the solution is thrown, said screencatching the salt and retaining the same as the solution drops back.

In processes of crystallizing aluminum sulphate out of solutions of thelatter, the step which consists in subjecting the solution in a vacuumtank to a vacuum of from twelve (12). to twenty-five (25) inches ofmercury, causing it to boil violently, means being superposed above theevaporating pan against which the solution is thrown, said meanscatching the salt and retaining the same as the solution drops back.

6. In processes'of crystallizingaluminum sulphate out of solutions ofthe latter, the step which consists in subjectingthe solution in avacuum tank to a vacuum of from twelve (12) to twenty-five (25) inchesof mercury, causing it to oil violently, a screen being superposed abovethe evaporating pan against which the solution is thrown, said screencatching the salt and retaining the same as the so ution drops back.

7. In processes of crystallizing aluminum sulphate out of solutionsofthe latter, the step which consists in subjecting the solution in avacuum'tank to a vacuum of from twelve (12) to twenty-five (25) inchesof mercury, steam being admitted to the tank to maintain a temperaturetherein of from 78 to 100 Fahrenheit, thus causing the solu-- tion toboil violently, means being superposed above the evaporating pan againstthe solution drops which the solution is thrown, said means catching thesalt and retaining the same as the solution drops back.

8. In processes of crystallizing aluminum sulphate out of solutions ofthe latter, the step which consists in subjecting the solution in avacuum tank to a vacuum of from twelve (12) to twenty-five (25) inchesof mercury, steam being admitted to the tank to maintain a temperaturetherein of from 78 to-100 Fahrenheit, thus causing the solution-@t'oboil violently, a screen being superposed 'above the evaporating panagainst which the solution is thrown,said screen catching the salt andretaining the same as the solution drops back.

9. In processes of crystallizing aluminum sulphate out of solutions ofthe latter, the steps which consist in subjecting the solution in avacuum'tank to a vacuum of from twelve (12) to twenty-five inches ofmercury, steam being admitted to the tank to maintain a temperaturetherein of from 78 to 100 Fahrenheit, thus causing the solution to boilviolently, means being superposed above the evaporating pan againstwhich the solution is thrown, said means catching the salt and retainingthe same as the solution drops back; withdrawing the mother liquor fromthe tank; and then drying the suspended aluminum sulphate crystals bycreatiglgk a substantially perfect vacuum in the t 10: In processes ofproducing crystalline aluminum sulphate, the steps which consist inreacting between aluminum hydroxide and sulphuric acid; subjecting theresultant aluminum sulphate solution in a vacuum tank to a vacuum offrom twelve (12) to twenty-five (25) inches of mercury, causing thesolution to boil violently, the screen being superposed above theevaporating pan against which the solution is thrown, said screencatching the salt and retainin the same as the solution drops back; withrawing the mother liquor from the tank for reuse with another charge ofaluminum hydroxide; and then drying the suspended aluminum sulphatecrystals by creating a substantially perfect vacuum in the tank.

11. In processes of crystallizing aluminum sulphate out of solutions ofthe latter, the steps which consist in reacting between aluminumhydroxide and sulphuric acid; subjecting the resultant aluminum sulphateso lution in a vacuum tank to a vacuum of from twelve (12) totwenty-five (25) inches of mercury, steam being admitted to the tank tomaintain a temperature therein of from 78 to 100 Fahrenheit, thuscausing the solution to boil violently, a screen being superposed abovethe cvaporating pan, against which the solution is thrown, said screencatching the salt and retaining the same as the solution drops back;periodically withdrawing the mother liquor from the tankfor reuse withother charges of aluminum hydroxide; and drying the suspended aluminumsulphate crystals by creating a substantially perfect vacuum in thetank.

Signed by me this 4th day of May, 1922.

SHERMAN V. SCOFIELD. Signed by me this 13th day of May, 1922. JOHN B. LARUE.

